1. Field of the Invention
The present general inventive concept relates to an f-θ lens which scans a beam radiated from a light source onto an exposure body, a light scanning unit and an image forming apparatus employing the same, and more particularly, to an f-θ lens having an improved joining force during an joining process by a light curable joining type, a light scanning unit and an image forming apparatus employing the same.
2. Description of the Related Art
In general, a light scanning unit is employed for devices such as a laser printer, a digital photocopier, a facsimile, and so on. The light scanning unit forms a latent image on a photosensitive body through a main scanning by a beam deflector, and a sub scanning by rotation of a photosensitive body.
FIG. 1 is a schematic view illustrating an optical arrangement of a conventional light scanning unit. As illustrated in FIG. 1, the conventional light scanning unit includes a light source 1 which generates and radiates a beam, a beam deflector 7 which deflects an incident beam so that the beam radiated from the light source 1 can be main-scanned onto a photosensitive body 15, and an f-θ lens 21 which corrects an error included in the beam deflected by the beam deflector 7. Also, on an optical path between the light source 1 and the beam deflector 7 are further provided a collimating lens 3 which collimates the beam radiated from the light source 1, and a cylindrical lens 5 which shapes the collimated beam. Between the f-θ lens 21 and the photosensitive body 15 is disposed a reflecting mirror 13 which changes a direction of the scanned beam.
The beam deflector 7 includes a driving source 9, and a rotational polygon mirror 8 rotated by the driving source 9. Accordingly, the beam radiated from the light source 1 changes its direction according to rotation of the rotational polygon mirror 8 and its scanning direction is determined.
The f-θ lens 21 includes only a singular lens so as to reduce the number of parts and a manufacturing cost. In this case, astigmatism included in the beam deflected by the beam deflector 7 is corrected, and the scanning line is corrected to maintain an isometric line and isometric angle through the f-θ lens 21 including the singular lens above-described.
However, for this purpose, the f-θ lens 21 must have a thicker lens in comparison with a conventional f-θ lens including two lenses. Thus, a lens part 23 in the f-θ lens 21 for image-forming of the scanning beam has a thicker thickness than in a conventional f-θ lens including two lenses. Also, a joining part 25 which is extended from the lens part 23 to be joined to a mount (see 31 in FIG. 2) has a relatively thicker thickness H so as to stably support the lens part 23.
Meanwhile, the f-θ lens 21 should be installed in the mount 31 having the same configuration as that illustrated in FIG. 2 so as to dispose the above-described optical arrangement.
FIG. 2 is a schematic view showing a joining process employing an ultraviolet ray curable resin of the conventional f-θ lens.
As shown in FIG. 2, the joining part 25 is installed on the mount 31. At this time, between the mount 31 and a joining face 25a of the joining part 25 is spread an ultraviolet curable bond 33 which is cured by ultraviolet ray. After that, an ultraviolet ray L is emitted through an opposite face 25b of the joining part 25. Here, the ultraviolet ray L is emitted through an optical fiber 35 or a light source (not shown) disposed to face the opposite face 25b of the joining part 25.
A first portion L1 of the emitted ultraviolet ray passes through the joining part 25 to be emitted on the ultraviolet curable bond 33, and a second portion L2 of the emitted ultraviolet ray is absorbed inside the joining part 25, and a third portion L3 of the emitted ultraviolet ray is surface-reflected on the opposite face 25b of the joining part 25.
Accordingly, since the thickness of the joining part 25 is relatively thicker if the f-θ lens 21 is joined to the mount 31 in the above-described method, such absorption and surface-reflection in the joining part 25 cause a large light loss, thereby depreciating a joining efficiency.
Therefore, a facility cost factor may be generated since an ultraviolet emitting unit and an ultraviolet lamp which have more large light quantity and capacity are needed so as to join the f-θ lens, and also, if an ultraviolet emitting time is increased so as to obtain a predetermined hardness, an assembling time for joining is increased, thereby depreciating productivity.